Optionally... an animated GIF can be used for frame playback with no audio, not a great experience but works fine as long as text transcripts are available to accompany. Not really a serious way to transfer video though, just a desperate fallback (and was once upon a time the only way to simulate video on a phone).

By my heinously imprecise math, the right combination of these should reach about 90% of internet users (2B) and 50% of mobile devices with video and/or internet capabilities (0.8B), which would be 2.8 Billion people.

NOTE: Omitting "poster" attribute of HTML5 tag lets us also reach those few iOS users who haven't upgraded from iOS3 versions, which had a player bug with poster was used.

NOTE2: Likewise, turning off autoplay on all the players has two purposes, firstly we will only stream when we are sure the user wants to watch the video, secondly it avoids multiple players starting automatically on page load (which would require alot of obtrusive Javsacript and player juggling to prevent from happening).